A number of additive manufacturing technologies presently exist for the rapid creation of models, prototypes, and parts for limited run manufacturing or other applications. Such parts can be made using solid freeform fabrication techniques, which include but are not limited to stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, film transfer imaging, and the like. Some, but not all, of these techniques are performed by three-dimensional modelers that provide a layer of solidifiable liquid material and project a two-dimensional image of actinic radiation upon the material to selectively cure the material to define a cross-sectional area of the part to be produced. This process of providing layers of solidifiable liquid material and selectively curing the material with actinic radiation is repeated until a part is produced. As used herein, “actinic radiation” includes any and all electromagnetic radiation that produces a photochemical reaction in the material that is exposed to the electromagnetic radiation. Such actinic radiation includes, but is not limited to, radiation that results in cross-linking of any radiocrosslinkable material that absorbs the radiation. Examples of actinic radiation include, but are not limited to ultraviolet radiation, visible light, and infrared radiation.
Example three-dimensional modelers are disclosed in US Patent Publication Numbers 2008/0206383 and 2008/0169589 that are assigned to the present assignee and are incorporated by reference herein in their entireties. These three-dimensional modelers utilize the film transfer imaging technique to provide single layers of solidifiable liquid material proximate the image plane and selectively cure the material with actinic radiation projected from an imager. FIG. 1 illustrates such a prior art three-dimensional modeler 10 in which a single layer of solidifiable liquid material 12 is provided via a transfer film 14 to proximate an image plane 16. The material 12 is supplied in a replaceable cartridge 18. An imager (see imager 20 of FIG. 2) projects a two-dimensional pattern of actinic radiation from beneath the image plane 16 and through the image plane and the film 14 to selectively cure the solidifiable liquid material 12 on the upper surface of the film.
After a pattern of material 12 corresponding to the respective cross-section of the part being produced has been selectively cured a desired amount, the build platform 22 (which is connected to the part being produced) is raised to separate the cured pattern of material from the film. The film and any uncured solidifiable liquid material 12 are returned to the cartridge and then the film is pulled another time across the image plane to once again provide a complete single layer of solidifiable liquid material proximate the image plane and the process is repeated until the part is produced.
As stated above, the imager projects a two-dimensional pattern of actinic radiation that corresponds to the respective cross-section of the part being produced. However, certain imagers do not project an equivalent amount of actinic radiation over the two-dimensional area of the image plane and/or the amount of actinic radiation that is projected by the imager diminishes over time. Therefore, three-dimensional modelers having such imagers may produce parts that possess undesirable part qualities (aesthetic and/or structural) resulting from over-curing and/or under-curing of the material selectively cured to form the part.